1. Field of the Invention
The present invention derives from the technical field of charge control agents, in toners and developers for electrophotographic recording processes and in powders and powder coatings for surface coating.
In electrophotographic recording processes a "latent charge image" is produced on a photoconductor, for example by charging a photoconductor by corona discharge and then subjecting the electrostatically charged surface of the photoconductor to imagewise exposure, which causes a discharge to the earthed substrate on the exposed areas. The "latent charge image" thus produced is then developed by applying a toner. In the next step, the toner is transferred from the photoconductor to, for example, paper, textiles, foils or plastic, and is fixed, for example by means of pressure, radiation, heat or the effect of solvent. The used photoconductor is then cleaned and is ready for a new recording process.
Numerous patents describe the optimization of toners, and investigate the effect of the toner binder (variation of resin/resin components or wax/wax components), the effects of carriers (in two-component developers) and of magnetic pigments (in one-component developers).
One measure of the quality of a toner is its specific charge q/m (charge per unit mass). In addition to the sign and level of the electrostatic charge, the principal, decisive quality criteria are the rapid attainment of the desired charge level and the constancy of this charge over a relatively long activation period. This is of central importance in practice insofar as the toner in the developer mixture may undergo activation for a considerable period before being transferred to the photoconductor, since in some cases it remains in the developer mixture for a period covering the production of up to several thousand copies. In addition to this, the insensitivity of the toner to climatic effects such as temperature and atmospheric humidity is a further important criterion for its suitability.
2. Description of the Prior Art
Both positively and negatively chargeable toners are used in copiers and laser printers, depending on the type of process and type of apparatus.
To obtain electrophotographic toners or developers having either a positive or a negative charge, it is common to add so-called charge control agents. In this context it is not only the sign of the charge control but also the extent of the control effect which is important, since higher activity allows a smaller amount to be used. Since the charge of toner binders is generally heavily dependent on the activation period, the function of a charge control agent is, on the one hand, to set the sign and level of the toner charge and, on the other hand, to counteract the charge drift of the toner binder and to ensure a constant toner charge.
Charge control agents which are not able to prevent the toner or developer showing a high charge drift (aging) during a prolonged period of use, and which may even cause the toner or developer to undergo charge inversion, are therefore unsuitable for use in practice.
Full-color copiers and laser printers operate according to the principle of trichromatism, necessitating exact color matching of the three primary colours (yellow, cyan and magenta). The slightest shift in hue of even only one of the three primary colours urgently requires a shift in hue of the two other colors, so as to enable necessarily full-color copies and prints which are true to the original to be produced in this case too. Because of this precise matching of the color properties of the individual colorants to one another in color toners, it is especially important that charge control agents do not have an inherent color.
In color toners, in addition to the precisely defined requirements in terms of color, the three toners yellow, cyan and magenta must also be matched exactly to one another in terms of their triboelectric properties. This triboelectric matching is required because, in full-color printing or in full-color copying, the three color toners (or four color toners if black is included) have to be transferred in succession in the same apparatus.
It is known that colorants may in some cases have a sustained effect on the triboelectric charge of toners (H.-T. Macholdt, A. Sieber, Dyes & Pigments 9 (1988), 119-127). Because of the different triboelectric effects of colorants and the resulting effect, sometimes very pronounced, on toner chargeability, it is not possible simply to add the colorants to a toner base formulation made available at the start. On the contrary, it may be necessary to make available for each colorant an individual formulation to which the nature and amount of the required charge control agent are tailored specifically. This procedure is, accordingly, laborious and, in the case of color toners for the three-color process, represents a further difficulty in addition to those already described.
Consequently, highly effective, colorless charge control agents are required which are able to compensate for the different triboelectric characteristics of different colorants and to give the toner the desired charge. In this way, colorants which are very different triboelectrically can be employed in the various toners required (yellow, cyan, magenta and if desired black) using one and the same charge control agent, on the basis of a toner base formulation made available at the start. Another important practical requirement is that the charge control agents should have high thermal stability and good dispersibility. Typical temperatures at which charge control agents are incorporated into the toner resins, when using headers or extruders, are between 100.degree. C. and 200.degree. C. Correspondingly, thermal stability at 200.degree. C., and better still at 250.degree. C., is a great advantage. It is also important for the thermal stability to be ensured over a relatively long period (about 30 minutes) and in a variety of binder systems. This is significant because matrix effects occur again and again and lead to the premature decomposition of the charge control agent in the toner resin, causing the toner resin to turn a dark yellow or dark brown color and the charge control effect to be wholly or partly lost. Typical toner binders are resins polymerization, polyaddition and polycondensation resins, such as styrene, styrene-acrylate, styrene-butadiene, acrylate, polyester, phenolic and epoxy resins, individually or in combination, which may also contain further components such as colorants, waxes or flow assistants, or may have these components added subsequently.
It is of great advantage for its good dispersibility if the charge control agent has, as far as possible, no waxlike properties, no tackiness, and a melting or softening point of &gt;150.degree. C., preferably &gt;200.degree. C. Tackiness frequently causes problems during metered addition to the toner formulation, and low melting or softening points may lead to inhomogenous distribution during dispersion, caused by the material coalescing in drops in the carrier material.
Apart from their use in electrophotographic toners and developers, charge control agents may also be used to improve the electrostatic charge of powders and coatings, especially in triboelectrically or electrokinetically sprayed powder coatings as are used to coat surfaces of articles made from, for example, metal, wood, plastic, glass, ceramics, concrete, textile material, paper or rubber. Powder coating technology is used, for example, when coating small articles, such as garden furniture, camping equipment, household implements, automobile components, refrigerators and shelving, and for coating workpieces of complicated shape. The powder coating or the powder receives its electrostatic charge, in general, according to one of the two following processes:
a) in the corona process, the powder coating or the powder is guided past a charged corona and in so doing is charged; PA1 b) in the triboelectric or electrokinetic process, the principle of frictional electricity is utilized. PA1 a) copolymerization of salts, preferably halides, of monomeric diallylammonium components of the formula (I) ##STR2## with sulfur dioxide or a compound which liberates sulfur dioxide, and b) anion exchange, the anions, preferably the halide ions, of the diallylammonium components being completely or partially replaced by the anions A, the diallylammonium components in each case cyclized to give a five- or six-membered ring and being connected to one another by one or more divalent radicals --SO.sub.2 -- to form polymers, the polysulfonyldiallylammonium salts having a molecular weight of between 500 and 5,000,000, the ratio of the number of diallylammonium components to the number of divalent SO.sub.2 radicals being from 1:0.01 to 1:100, PA1 or of an organic anion, preferably a phenolate, olefinic, aliphatic or aromatic carboxylate, thiolate, sulfonate or sulfate in which the alkyl, alkenyl or aryl radicals may also be perfluorinated; or of a disulfo-pyrrolidinium betaine of the formula (III) ##STR4## R.sub.1 ' and R.sub.2 ' having the meanings given for R.sub.1 and R.sub.2 and X and Y each being a straight-chain or branched aliphatic, saturated or unsaturated alkylene(C.sub.1 -C.sub.18) radical or alkoxylene(C.sub.1 -C.sub.18) radical; PA1 or A is a combination of the abovementioned anions; individually or in combination as charge control agents in electrophotographic toners and developers which are employed for copying and reproducing originals and for printing electronically, magnetically or optically stored information or in colorproofing, and as charge control agents in powders and powder coatings. PA1 R.sub.1 to R.sub.12 are identical or different and are hydrogen atoms, straight-chain or branched, saturated or unsaturated alkyl (C.sub.1 -C.sub.8) or alkoxy (C.sub.1 -C.sub.8) radicals, phenyl, naphthyl or pyridyl, tolyl, methoxyphenyl, benzyl, cyclopentyl or cyclohexyl, or in which the radicals R.sub.1 and R.sub.2 are substituted by one or more halogen atoms or by one or more of the radicals hydroxyl, carboxyl, sulfo, --NH--C(O)-alkyl(C.sub.1 -C.sub.4), --NH--SO.sub.2 -alkyl(C.sub.1 -C.sub.4), --C(O)-alkyl(C.sub.1 -C.sub.4), --NH.sub.2, --NH[alkyl(C.sub.1 -C.sub.4)], --N[alkyl(C.sub.1 -C.sub.4)].sub.2, nitro, alkylene(C.sub.2 -C.sub.4)-O-alkyl(C.sub.1 -C.sub.4), alkyl (C.sub.1 -C.sub.4), alkoxy(C.sub.1 -C.sub.4), phenoxy, haloalkyl (C.sub.1 -C.sub.4), haloalkoxy (C.sub.1 -C.sub.4) or --C(O)O-alkyl(C.sub.1 -C.sub.4), PA1 the molecular weight is between 1000 and 1,000,000 and the ratio of the number of diallylammonium components to the number of divalent SO.sub.2 radicals is from 1: 0.1 to 1:10. PA1 in component (2) A has the meaning BF.sub.4 ', PA1 in component (3) A has the meaning B(C.sub.6 H.sub.5).sub.4.sup.-, PA1 in component (4) A has the meaning PF.sub.6.sup.-, PA1 in component (5) A has the meaning 1,1 -dialkyl - 3,4 -disulfomethylpyrrolidinium betaine, PA1 in component (6) A has the meaning P(Mo.sub.3 O.sub.10).sub.4.sup.3-, PA1 in component (7) A has the meaning CF.sub.3 SO.sub.3.sup.-, PA1 in component (8) A has the meaning HSO.sub.4.sup.-, PA1 in component (9) A has the meaning Cl.sup.-, PA1 and any desired mixtures or mixed crystals of polysulfonyldiallylammonium salts which contain two or more of components (2) to (9); PA1 the molecular mass of the polysulfonyldiallylammonium salts is between 1000 and 500,000 and the ratio of the number of diallylammonium components to the number of divalent SO.sub.2 radicals is 1:1. Also particularly preferred are mixtures or mixed crystals of polysulfonyldiallylammonium salts which contain two or more of components (2), (3), (4) and (7). PA1 a) copolymerization of salts, preferably halides, of the monomeric diallylammonium components of the formula (I) with sulfur dioxide or a compound which liberates sulfur dioxide, the diallylammonium cations being cyclized predominantly to form a pyrrolidinium ring and being connected to one another by one or more of the divalent radicals -SO.sub.2 - to form polymers, and PA1 b) anion exchange, the anions, preferably the halide ions, of the diallylammonium components being completely or partially replaced by the anions A mentioned below, the polysulfonyldiallylammonium salts having a molecular weight of between 500 and 5,000,000, preferably between 1000 and 1,000,000, in particular between 1000 and 500,000, the ratio of the number of diallylammonium components to the number of divalent radicals -SO.sub.2 - being from 1:0.01 to 1:100, preferably from 1:0.1 to 1:10, in particular 1:1, and PA1 the radicals R.sub.1 to R.sub.12 in formula (I) being defined as described above and the anion A being the stoichiometric anion equivalent of a heteropolyacid; of a borate of the formula (II); of a disulfopyrrolidinium betaine of the formula (III); of an organic anion; or of an inorganic anion with the exception of chloride. PA1 a) dissolving a polysulfonyldiallylammonium halide which has been prepared, for example, in accordance with EP-A-251,558 and in which the halide is fluoride, chloride, bromide or iodide, preferably chloride or bromide and particularly preferably chloride, in water or in a mixture of water and an organic solvent which is completely or partly miscible with water, PA1 b) adding to the solution prepared in a) one or more compounds forming the basis for the anion A, preferably the sodium salt of the anion A, at a temperature of between 0.degree. C. and 100.degree. C., preferably between 10.degree. C. and 70.degree. C., and at a pH of between 3 and 10, preferably between 5 and 8, and PA1 c) then precipitating the resulting polysulfonyldiallylammonium salt, if necessary, by salting it out with a halogen-containing salt, for example potassium chloride. The polysulfonyldiallylammonium salts are often so insoluble in water or in the stated water/solvent mixture that they precipitate from the solution even without additional salting out. PA1 d) after precipitation, largely freeing the precipitated polysulfonyldiallylammonium salts from inorganic salts, especially from sodium chloride or potassium chloride, by a suitable method, for example by washing or by a reverse osmosis procedure, and subsequently PA1 e) drying in vacuo at elevated temperature, preferably at from 70.degree. C. to 100.degree. C.
In the spray apparatus, the powder coating or the powder receives an electrostatic charge which is opposite to the charge of its friction partner, generally a hose or spray tube made, for example of polytetrafluoroethylene. It is also possible to combine the two processes.
Typical powder coating resins employed are epoxy resins, polyester resins containing carboxyl and hydroxyl groups, polyurethane resins and acrylic resins, together with the conventional curing agents. Combinations of resins are also used. For example, epoxy resins are often employed in combination with polyester resins containing carboxyl and hydroxyl groups. Examples of typical curing agent components for epoxy resins are acid anhydrides, imidazoles and dicyandiamide, and derivatives thereof. Examples of typical curing agent components for polyester resins containing hydroxyl groups are acid anhydrides, blocked isocyanates, bisacylurethanes, phenolic resins and melamine resins. Examples of typical curing agent components for polyester resins containing carboxyl groups are triglycidyl isocyanurates or epoxy resins. Typical curing components used in acrylic resins are, for example, oxazolines, isocyanates, triglycidyl isocyanurates or dicarboxylic acids.
The disadvantage of insufficient charge can be seen above all in triboelectrically or electrokinetically sprayed powders and powder coatings which have been prepared using polyester resins, especially polyesters containing carboxyl groups, or using so-called mixed powders, also referred to as hybrid powders. Mixed powders are powder coatings whose resin base comprises a combination of epoxy resin and polyester resin containing carboxyl groups. Mixed powders form the basis of the powder coatings used most commonly in practice. Inadequate charging of the abovementioned powders and powder coatings results in inadequate throwing powder and an inadequate deposition rate on the workpiece to be coated. The term "throwing power" is a measure of the extent to which a powder or powder coating is deposited on the workpiece to be coated, including its rear faces, cavities, fissures and, in particular, its inner edges and angles.
Colorless charge control agents are claimed in numerous patents. However, the colorless charge control agents of the prior art have a range of disadvantages which severely limit their use in practice and even, in some cases, render it impossible. For instance, the complexes of chromium, iron, cobalt and zinc described in U.S. Pat. No. 4,656,112 also have the disadvantage, in addition to the problem of the heavy metals, that they are in some cases not actually colorless and may consequently be of only limited application in color toners or in white or colored powder coatings. The known quaternary ammonium compounds, which are suitable in principle, are often difficult to disperse, resulting in nonuniform charging of the toner. In addition, a problem which often occurs is that the toner charge produced by these compounds is not stable over a prolonged activation period (up to 24 hours), especially at high temperature and atmospheric humidity, which then leads in the course of a copying or printing process to the accumulation of incorrectly or insufficiently charged toner particles and thus brings the process to a standstill.
Furthermore, it is known that charge control agents based on ammonium and immonium compounds are sensitive to light or mechanical effects (U.S. Pat. No. 4,683,188) and may be thermally labile, and that they form decomposition products which may have an adverse effect on the triboelectric charging of the toner (U.S. Pat. No. 4,684,596) and/or have a strong inherent color, often dark brown. In addition to this, they are often waxlike, and some are water-soluble and/or possess a low effectiveness as charge control agents.
Although suitable in principle, charge control agents based on high-grade fluorinated ammonium and immonium compounds (U.S. Pat. No. 5,069,994) have the disadvantage of a complex synthesis, resulting in high preparation costs for the corresponding substances, and are not sufficiently stable to heat. As charge control agents, phosphonium salts are less effective than ammonium salts (U.S. Pat. No. 4,496,643) and may cause toxicological problems. Charge control agents based on polymeric ammonium compounds (DE-A-4,029,653) lead in some cases to an amine odor of the toner or developer, and the charge control characteristics of these substances can be altered by relatively mild oxidation and the absorption of moisture. Furthermore, the oxidation products are colored and are consequently interfere, especially in color toners. The abovementioned charge control agents for electrophotographic toners and developers, because of their colored nature, are unsuitable for use in the predominantly white or clear triboelectrically or electrokinetically sprayed powders and powder coatings. In addition, inadequate thermal stability severely restricts the use of such charge control agents, since powder coatings, for example, are baked on at over 200.degree. C. for 15 minutes. The charge control agents for powders and powder coatings, which are claimed in U.S. Pat. No. 5,069,994, are difficult to handle because of their waxy nature and water solubility or hygroscopic nature, and are of only limited applicability.